The invention is in the field of Semiconductor-On-Insulator (SOI) devices, and relates specifically to lateral SOI devices for high-voltage and power applications.
In fabricating high-voltage power devices, tradeoffs and compromises must typically be made in areas such as breakdown voltage, size, "on" resistance and manufacturing simplicity and reliability. Frequently, improving one parameter, such as breakdown voltage, will result in the degradation of another parameter, such as "on" resistance. Ideally, such devices would feature superior characteristics in all areas, with a minimum of operational and fabrication drawbacks.
One category of power devices that has shown considerable promise uses a semiconductor (usually silicon) layer provided on an insulating layer in a lateral configuration. A typical lateral double-diffused MOS (LDMOS) transistor in an SOI configuration is shown in U.S. Pat. No. 5,059,547. Such devices, although an improvement over earlier devices, are still a compromise in terms of the tradeoff between breakdown voltage and "on" resistance.
An improvement over the basic SOI structure, in which increased breakdown voltages are achieved by providing a linear doping profile in the drift region, is shown in U.S. Pat. No. 5,246,870 and related U.S. patent application Ser. No. 08/015,061, filed Feb. 8, 1993, now U.S. Pat. No. 5,300,448, both commonly owned with the instant application. In these SOI devices, the drift region between the channel and drain in a lateral MOS structure is provided with a linear lateral doping density profile, an expedient which results in substantially increased breakdown voltage characteristics.
A further improvement in the operating characteristics of SOI devices has been attempted by fabricating devices in wide bandgap materials such as silicon carbide (SIC). In U.S. Pat. No. 4,983,538, for example, a conventional MOSFET is shown in a silicon carbide layer on an insulator. However, as noted in that Patent, the use of SiC entails various manufacturing problems and complexities, and such materials are still not commercially feasible for fabricating lateral SOI power devices.
Accordingly, it would be desirable to have a lateral SOI device having a drift region of a wide bandgap semiconductor material in order to obtain superior operational characteristics, in a device configuration which is commercially feasible for manufacture using known processing technology.